Vice President Joseph R. Biden said Wednesday the U.S. and its allies must impose additional sanctions on Russia if it interferes with Ukrainian elections scheduled for Sunday.

Speaking alongside Romanian President Traian Basescu, the vice president said election day in Ukraine — the first since the country was plunged into chaos and violence and saw Russian troops mass along its eastern border — represents a pivotal moment.

“Sunday is election day in Ukraine … And it’s a chance for Ukrainians to decide their own future,” Mr. Biden said. “All countries in Europe, all countries should use their influence to promote a stable and positive environment so the Ukrainian citizens can cast their ballots freely. The president and I have agreed that if Russia undermines these elections on Sunday, we must remain resolute in imposing greater cost on Russia.”

The U.S. already has targeted members of Russian President Vladimir Putin’s inner circle with economic sanctions, and has threatened to impose broader sanctions on entire sectors of the Russian economy, should Mr. Putin continue to meddle in Ukrainian affairs.

Mr. Putin has said he supports the Ukrainian elections on Sunday, but his claim that Russian troops are withdrawing from the Ukrainian border has been disputed by the U.S. and international organizations such as NATO.